We've come to one of the coldest spots on Earth to search for beings that thrive in blistering heat. In a place with full daylight for four months, we're seeking life that dwells in utter darkness. Welcome to the topsy-turvy world of Antarctica's Mt. Erebus.

A mix of ropes and ladders eases access to Warren Cave, a labyrinth of passages melted from the ice by the volcano's heat. Small currents of air probably cause the scalloping around the cave's entrance.

A study in contrasts: ice and snow in the foreground, the lava lake of Mount Erebus below. Erebus is one of just a handful of volcanoes to boast a permanent lava lake. At the moment this picture was taken, the volcano was quiet, but it frequently erupts, hurling lava bombs high in the air.

On a clear evening the main crater of the volcano is quiet, exuding just a few puffs of steam. Abutting it is another crater, now extinct. Beyond, a dreamscape of sea ice and ocean stretches to the mountains and dry valleys of the Antarctic mainland.

It's midnight, but with the light so bright, it's hard to stop exploring the ice towers. This is one of the biggest on Erebus, but the flux of heat and moisture from below has collapsed its side. In the distance, beyond another ice tower, the Hut Point Peninsula extends like a finger toward Mount Discovery.

Inside the ice caves the volcano's warm, wet air freezes into frost crystals that grow into different shapes, depending on how the air currents flow. Here, a team member investigates the passages of Hut Cave.

Stu Arnold of the research support agency Antarctica New Zealand steadies a drill bit, while microbiologist Craig Cary drives it into an ice-tower wall. Moments later, cries of delight: They have a perfect ice core. They hope it will contain microbes lofted from deep within the volcano and frozen in the tower ice.

Microbiologist Craig Cary checks his notes underneath the blue dome of an ice cave, where he will take a soil sample to check for microbes. The blue light filters through the thin ice above the cave, which is close to the surface. Anyone walking outside the cave must take care or risk falling through.

An exquisite crystal hangs in Warren Cave. Similar ones form in your tent at night—the stream of air from your lungs freezes when it hits the tent wall, and you wake to find that a profusion of frost crystals has grown above your head.

Frost crystals form when warm, moist air hits a cold surface, then grow into different shapes depending on how the air currents flow. They are fragile: A person simply walking past can create enough of a breeze for crystals to change shape or vanish. And they are astoundingly beautiful, especially in Warren Cave. In the dark passages away from the entrance, festoons of ice crystals glitter and sparkle before your flashlight.

On Mount Erebus the weather can change rapidly. After a day of clear skies and unlimited visibility, a storm swept in, and for the next 15 hours, the temperature dropped below minus 40°F. Winds of 45 miles an hour or more hurled ice crystals at the expedition tents, building deep drifts around them.

Microbiologists collect samples from the volcano's hot soils. The white suits afford protection—not for the humans but for the resident organisms of the hot soils, preventing foreign life-forms from being accidentally introduced into these unusual ecosystems. Though the ground is steamy hot, this is cold work; the air temperature is more than 150°F colder than the soil temperature.

The microbiology team gets ready to sample the volcano's hot soils. To protect the resident life-forms from invasive ones, the researchers spray their boots with ethanol to remove any contaminants and wear sterile suits over their cold-weather gear—giving them the look of monstrous snowmen.

An unearthly landscape. On the upper slopes of Mount Erebus, the ice has been polished and textured by the wind. In the distance, sea ice, open ocean, and the mountains and dry valleys of the Antarctic mainland. Three figures—tiny in this vast place—prepare to return to camp after a cold day's work.

Steam swirls out of the Erebus crater, bringing with it a stench of sulfur. The inside of the crater looks like an exotic cheese, layers of ice alternating with layers of dark volcanic rocks, soils, and clays. The power of nature is strong here: thin air and fierce cold plus the elemental force of an active volcano.